1. Field of the Invention
The present invention relates to gas separation membranes prepared by reacting aromatic tetracarboxylic dianyhydrides with from 20 to 80 mol % of methylene dianilines having alkyl substituents on all positions ortho to the amine functions and 20 to 80 mol % aromatic diamines which are unsubstituted.
2. Prior Art
U.S. Pat. No. 4,838,900 discloses gas separation membranes formed from alkyl substituted methylene bisanilines and aromatic dianhydrides.
U.S. Pat. No. 4,705,540 discloses rigid polyimide gas separation membrane materials prepared from alkyl-substituted phenylene diamines and structurally rigid aromatic tetracarboxylic dianhydrides. Membranes prepared from these materials have exceptionally high gas permeation rates with moderate gas selectivities.
U.S. Pat. No. 4,717,394 discloses that a greater range of gas separation membrane productivities could be achieved through the controlled addition of less chain rigidity in the polyimide forming the membrane than that found for U.S. Pat. No. 4,705,540.
U.S. Pat. Re. No. 30,351; U.S. Pat. No. 3,822,202 and U.S. Pat. No. 3,899,309 disclose gas separation membranes comprising certain semi-rigid aromatic polyimides, polyamides and polyesters.